The present invention relates to a light modulator device for a display, said light modulator device comprising at least one spatial light modulator and at least one controllable diffraction device, said components being controllable by a control unit, with the display being designed for a three-dimensional representation of images of a 3D scene.
The field of application of the present invention includes displays with an observer window, for example holographic or autostereoscopic displays, where a 3D scene is encodable, for example, in a hologram or where the stereoscopic images of the 3D scene are representable two- and/or three-dimensionally. Observers can perceive the 3D scene as a holographic reconstruction or as a stereo image if at least one observer window coincides with the positions of observer eyes.
With a holographic display, the observer can see a reconstructed scene of an object in a reconstruction space which is spanned by the observer window and the screen if an observer window coincides with the eye pupil. The eye pupil is situated at a certain eye position for which the reconstruction must be generated. However, if the observer moves sideways or along the optical axis of the display, the observer window will no longer coincide with the eye pupil of the observer and, consequently, the observer will not be able to see the complete reconstruction any longer. To enable the observer to see the complete reconstruction again, the position of the observer window must be matched again to the new position of the eye pupil (eye position).
In this respect, it is known in the prior art, for example from documents DE 10 2005 023 743 A1 or WO 2007/131817 A1, the entire contents of both of which being fully incorporated herein by reference, to move the observer window laterally and/or axially to the new eye position with the help of a deflection element. When doing so, the size of the observer window for the new eye position must be adapted in a defined way depending on its distance to a reference plane, which can, for example be the plane of the controllable light modulator.
A number of documents, for example DE 10 2008 043 620 A1 or WO 03/019952 A1, the entire contents of both of which being fully incorporated herein by reference, describe autostereoscopic displays where 3D scenes can be represented three-dimensionally and where these scenes can be seen by at least one observer through observer windows, which are also referred to as sweet spots. Observer windows can be generated at changing observer eye positions here, too.
In an autostereoscopic display, the reflection angle of the light sources determines the size of the observer window, which is formed by imaging the light sources into the observer plane by a lens array. If the axial distance to a reference plane (e.g. the surface of the display or light modulator) changes, then the size of the observer window is known to change as well, thereby possibly inducing the problem of the observer windows for two different eyes overlapping, disturbing the perception of the three-dimensional representation by the individual observers. If the observer window becomes smaller, there might be the problem that the 3D scene cannot completely be perceived three-dimensionally.
The same applies if the holographic display is operated with a 1D encoding method in a single-parallax mode and an observer window having the size that corresponds with the size of an eye pupil is to be generated in the incoherent direction.
Further, an autostereoscopic or holographic display is required to be designed such that can be switched from the 3D (three-dimensional) mode to the 2D (two-dimensional) mode. To do so, a switchable diffusor (light scattering element) is additionally disposed in the optical path; see for example document U.S. Pat. No. 5,897,184, the entire contents of which being fully incorporated herein by reference. In the 3D mode, the diffusor can, for example, be in a transparent, non-diffusing state. The size of the observer window to be generated, which should at least correspond with the diameter of an eye pupil, is continuously adapted to the distance of a detected eye position and the display in the 3D mode.
In the 2D mode, the diffusor is switched to the diffusing state. The observer window should be at least that large that it covers both eyes of an observer or even all eyes of all observers. Additional optical elements, such as a switchable diffusor or the above-mentioned deflection elements, make a display for the representation of three-dimensional image contents more complicated, more expensive and more susceptible to faults.
A switchable diffusion element as such is known, for example, from the international patent application PCT/EP2010/058625 (WO 2010/149587 A2), the entire contents of which being fully incorporated herein by reference.